1. Technical Field
The present invention relates generally to the production of airfoil-shaped structures and specifically to the production of a superplastically formed/diffusion bonded airfoil-shaped structure having a structurally reinforced, contoured leading edge.
2. Background Art
Certain metals and metal alloys develop unusually high tensile elongations with minimum necking when deformed within specific temperatures and specific strain rate ranges. This characteristic, known as superplasticity, is known in the art as applied to the production of complex shapes. It is also known in the art that at these superplastic forming temperatures the same metals and metal alloys can be diffusion bonded with the application of pressure contact surfaces. A well known superplastic forming process is disclosed in U.S. Pat. Nos. 4,217,397 entitled "Metallic Sandwich Structure and Method of Fabrication" which issued to Hayase et al. on Aug. 12, 1980; and 4,304,821 entitled "Method of Fabricating Metallic Sandwich Structure" which issued to Hayase et al. on Dec. 8, 1981. The patents disclosing this superplastic forming process, commonly known as the "four sheet process", have been assigned to the assignee of the present invention, and are herein incorporated by reference.
Techniques for superplastic forming and diffusion bonding (SPF/DB) airfoil-shaped structures having contoured leading edges typically have employed a conventional four sheet process. Using the four sheet SPF/DB process generally requires a cost and additional time required to remove (i.e., trim, fusion weld, grind and polish) the weld seam created across the leading edge.
It is further known in the art to produce structures having contoured leading edges by employing the SPF/DB process without the conventional four sheet process. Although a weld seam across the leading edge is not created with this process, it often requires controlling multiple forming pressures. Use for larger airfoil structures sometimes is limited with this process. Examples of this SPF/DB process are disclosed (and incorporated by reference herein) in U.S. Pat. Nos. 5,240,376 entitled "SPF/DB Hollow Core Fan Blade" which issued to Velicki on Aug. 31, 1993; and 5,384,959 entitled "Method of Making a SPF/DB Hollow Core Fan Blade" which issued to Velicki on Jan. 31, 1995, each of which is assigned to the assignee of the present invention.